Variable capacitance diode, step recovery diode, bidirectional trigger diode
Varactor is a nonlinear capacitor composed of PN junction capacitance and external bias voltage. It is widely used in parametric amplifiers, electronic tuning and frequency doubling circuits. Variable diode mainly through a series of structural design, process design and other methods to highlight the nonlinear relationship between capacitance and voltage, improve the Q value for supply. The structure of varactor is similar to the structure of ordinary diode.
Step recovery diode
Step recovery diode (SRD) is a special type of varactor diode, also known as charge storage diode, called step diode. It has very high nonlinear reactance. Its application in frequency multiplier is unique. High frequency doubling can be achieved by utilizing the abundant harmonics contained in the fast mutation of reverse current recovery. It is an excellent frequency doubling element in the microwave field.
The characteristic of stepping tube is based on the special distribution of impurities in PN junction. Similar to varactor diodes, the circuit symbols of step transistors have the same DC voltage ampere characteristics as ordinary PN structure step transistors.
The characteristic of the ladder tube is that when the diode in turn-on state is suddenly applied to the reverse voltage, the instantaneous reverse current immediately reaches the maximum value of IR, and maintains for a certain period of time, then immediately returns to zero.
Bidirectional trigger diode consists of three layers of silicon NPN. It is a symmetrical semiconductor transistor device, which is equivalent to base open circuit, collector and emitter NPN transistor.
When the input voltage is less than the rotary voltage, the tube is not connected and the current is very small. Once the transmission voltage equals the turn voltage, the tube is connected and the current rises rapidly, indicating negative resistance characteristics.
The bidirectional trigger diode has simple structure and low price. It is usually used to trigger bidirectional thyristors, or to form an overvoltage protection circuit.